The present invention is directed to a process and apparatus for the production of light conducting fibers which have a low degree of attenuation and a high numerical aperture. The glass fiber is coated with an optically active synthetic casing or cladding.
Low attenuation light conducting fibers having a high numerical aperture are currently produced by a glass, plastic process in which commercially available quartz glass rods are drawn to form fibers at a temperature of approximately 2000.degree. C. and are then coated after drawing with an optically active synthetic casing material which generally consists of polysiloxane. A discussion of these methods are contained in an article by J. G. Grabmaier et al, "Preparation and Properties of Low-Loss Optical Fibers with Fused-Silica Core and Plastic Cladding", Siemens Forschungs-und Entwicklungsbereicht, Vol. 6, No. 5, 1977, pp. 314-319. The use of an extremely pure quartz glass rod as a fiber core material means that these fibers are relatively expensive and furthermore can only be produced in a specific length which is dependent upon the size of the rod. Thus, the process is a discontinuous process. Furthermore, during the fiber drawing process, particles of dust and dirt can pass from the heating zone to the quartz glass rod and to the fiber surface with the result of which the tensile strength of the fiber is considerably reduced and attenuation is increased. A discussion of these problems is contained in an article by H. Aulich et al, "Preparation of Optical Fibers of High Tensile Strength", Siemens Forschungs-und Entwicklungsbereicht, Vol. 7, No. 3, 1978, pp. 158-165.